In recent years, along with the development of the fuel injection equipment called an injector, the fuel injection timing and the fuel injection quantity or the air-fuel ratio are easily controlled to effectuate the higher output, lower fuel consumption, and cleaner exhaust gas. Particularly at the fuel injection timing, it is common to strictly detect the state of a suction air valve, typically the phase state of a camshaft to inject the fuel in accordance with the phase state. However, a so-called cam sensor for detecting the phase state of the camshaft is expensive, and not often employed especially in the two-wheeled vehicle because the cylinder head is large in size. Therefore, in JP-A-10-227252, an engine controller is offered in which the phase state of a crankshaft and the suction air pressure are detected to find the stroke state of a cylinder. Accordingly, the stroke state is found without detecting the phase of the camshaft, employing this conventional technique, whereby it is possible to control the fuel injection timing in accordance with the stroke state.
By the way, to control the fuel injection quantity injected from the fuel injection equipment as previously described, a target air-fuel ratio is set in accordance with the engine speed and the throttle opening, and an actual suction air quantity is detected and multiplied by an inverse of the target air-fuel ratio to calculate a target fuel injection quantity.
To detect the suction air quantity, a hot wire air flow sensor and a Karman vortex sensor are typically employed to measure the mass flow and the volumetric flow, respectively, although a volumetric body (serge tank) for suppressing the pressure pulsation is needed, or mounted at a position where counter-flowing air does not enter to remove the error factors due to counter-flowing air. However, most engines for two-wheeled vehicles are based on a so-called individual-suction system for each cylinder, or a single cylinder engine, whereby those requirements are often not fully satisfied, and the suction air quantity is not accurately detected, employing these flow sensors.
Also, detection of the suction air quantity occurs at the final stage of the suction stroke, or the early stage of the compression stroke, when the fuel is already injected, whereby the air-fuel ratio control with the suction air quantity is only made at the next cycle. Even though the driver accelerates the vehicle by opening the throttle in a period up to the next cycle, a torque or output corresponding to acceleration may not be obtained, because the air-fuel ratio is adjusted at the previous target air-fuel ratio, whereby the driver has a feeling of disorder not to attain full acceleration. To solve this problem, a throttle valve sensor or a throttle position sensor for detecting a state of throttle may be employed to perceive a driver's will of acceleration, but especially in the case of the two-wheeled vehicle, these sensors, which are large in size and expensive, are not employed, whereby the problem is not solved in the current situation.
Thus, the suction air pressure within a suction pipe of the engine is detected. A comparison is made between the suction air pressure at the same stroke in the same phase of the crankshaft at the previous cycle, namely, one cycle before, or before two rotations of the crankshaft in the four-stroke cycle engine, and the present suction air pressure, in which if its difference value is greater than or equal to a predetermined value, an accelerated state is decided, and the fuel injection quantity corresponding to the accelerated state is set up. More specifically, if the accelerated state is detected from the suction air pressure, the fuel is promptly injected. Further, the fuel injection quantity during acceleration may be set up in consideration of an operating condition of the engine. This is derived from the fact that the suction air pressure at the suction stroke or the exhaust stroke before it accords with the opening of the throttle valve. However, it is found that it may be difficult to detect the accelerated state from the suction air pressure, depending on the operating condition of the engine.
Also, to detect the phase state of the crankshaft as previously described, the crankshaft itself or a member rotating synchronously with the crankshaft is formed with the teeth around its outer circumference, whereby an approaching tooth is sensed by a magnetic sensor to send out a pulse signal, which is detected as a crank pulse. The crank pulses detected in this way are numbered to detect the phase state of the crankshaft. For this numbering, the teeth are often provided at irregular intervals. That is, the detected crank pulses are marked with the feature. And the phase of the crankshaft is detected from the featured crank pulse, and the stroke is detected by comparing the suction air pressures in the same phase during two rotations of the crankshaft, whereby the injection timing and the ignition timing are controlled in accordance with this stroke and the phase of the crankshaft.
However, at the start of the engine, for example, the stroke is not detected unless the crankshaft is rotated at least twice. Particularly at the early time of starting the engine in the two-wheeled vehicle with small displacement and one cylinder, the rotating state of the crankshaft is not stable and the state of the crank pulse is not stable, in which it is difficult to detect the stroke. To detect the accelerated state as previously described, the suction air pressure one cycle before is needed. Moreover, it is required that the suction air pressure occurs in the suction stroke or the exhaust stroke before it. Accordingly, if the suction air pressure starts to be stored after the stroke detection, and the accelerated state is detected employing the stored suction air pressure alone, as previously described, the suction air pressure before the stroke detection is not employed, causing a problem that detection of the accelerated state is delayed correspondingly.
The present invention is achieved to solve the above-mentioned problems, and it is an object of the invention to provide an engine controller for inhibiting the detection of the accelerated state when it is difficult to detect the accelerated state from the suction air pressure, and quickening the detection of the accelerated state at the start of the engine.